The invention relates to a millimeter wave, lumped element, varactor tuned oscillator, VCO.
A VCO is an oscillator whose output frequency is electronically controlled. In solid state VCO's, the electronic tuning capability is provided by a voltage controlled capacitive element, a varactor diode, that is an integral part of the VCO circuit. The magnitude of the frequency change that can be produced in the VCO is a function of the maximum to minimum capacitance ratio of the varactor and the undesired padding effect (reduction) on the varactor capacitance ratio by other capacitive elements in the circuit, including circuit and diode package parasitics. In an ideal situation, the varactor would be the only capacitive energy storing element in the circuit, and hence it would have maximum control of the VCO tuning range. In addition to the capacitance ratio of the varactor, the output (resistive) loading is another factor that reduces VCO tuning range. The effect of resistive loading, when tranformed to the terminals of the VCO active element, is to decrease the effective capacitance ratio of the varactor. Hence, a load should be lightly coupled to a VCO when maximum tuning range is a performance objective. These basic considerations in wide band tuning of a Gunn VCO have resulted in a maximum tuning range of 7% of center frequency, a .+-.2 GHz (gigahertz) tuning band at a center frequency of 57.5 GHz, in commercially available waveguide (distributed circuit) type VCO's, "CMW Series Wideband Electronically-Tuned Gunn Oscillators", Central Microwave Company, Maryland Heights, Mo., June 1988.
The present invention provides an ultrawideband, lumped element, varactor tuned millimeter wave VCO. In one embodiment, the VCO has a .+-.10 GHz tuning band at a center frequency of 56 GHz, which 20 GHz tuning band (35.7% range) is five times the tuning range available with existing Gunn VCOs in the same frequency band.